1. Field of the Invention
This invention relates to a switching power supply device, and in particular relates to a switching power supply device that experiences reduced switching loss; and to an inverter, converter, air conditioner, solar power controller, and automobile employing same.
2. Description of Related Art
In the past, there have been cases in which a MOS transistor parasitic diode is employed as a freewheeling diode in an inverter. In such cases, when electrical current flows back in the forward direction to the parasitic diode, and a power supply voltage is applied in the reverse direction to the parasitic diode, recovery current (reverse recovery current) flows to the parasitic diode, generating a large switching loss.
Japanese Laid-Open Patent Application 7-264876 discloses a method of preventing flow of recovery current by connecting a backflow prevention diode in the forward direction between a node on the high-voltage side and the drain of the MOS transistor, as well as connecting a freewheeling diode in the forward direction between the source of the MOS transistor and node on the high-voltage side.
Japanese Laid-Open Patent Application 2010-29019 discloses a method of preventing flow of recovery current by serially connecting two MOS transistors between a node on the high-voltage side and a node on the low-voltage side, and connecting a high-withstand-voltage freewheeling diode in the forward direction between a node on the low-voltage side and a node on the high-voltage side.
However, a problem encountered in Japanese Laid-Open Patent Application 7-264876 is that conduction loss is generated in the backflow prevention diode. A problem encountered in Japanese Laid-Open Patent Application 2010-29019 is that costs are high, due to the need to furnish two MOS transistors and a high-withstand-voltage freewheeling diode.